The following disclosure relates to semiconductor manufacturing methods. In particular, the following disclosure relates to a method to repair a transparent photomask.
Integrated circuits (ICs) are manufactured by transferring geometric patterns from photomasks to light-sensitive material known as “photoresist”. In particular, a geometric pattern is formed on a layer of photoresist on a semiconductor substrate by providing light through a photomask. The photomask includes a transparent substrate (e.g., quartz) that is partially covered with an opaque material (e.g., chrome). The portions of the transparent material covered with opaque material blocks light, while the remaining uncovered portions of the transparent substrate allow light to pass therethrough, such that the light passing through the photomask transfers a pattern to the photoresist. After the photoresist has been exposed in this fashion, the photoresist is developed to selectively remove portions of the photoresist which were exposed to (or not exposed to) light, depending on whether the photoresist has a negative or positive tone. In some instances, the underlying substrate can then be etched with the patterned photoresist in place and the photoresist layer can be subsequently removed. Multiple patterned layers can be built up on the IC in this fashion to fabricate overall IC design.
In some instances, however, a portion of the pattern of opaque material does not form on the photomask due to errors with the photomask manufacturing process. As a result, if the incomplete pattern is transferred to the photoresist on the wafer, the resultant IC will be patterned incorrectly, and will likely fail to meet design specifications. Several methods of photomask repair may be used to replace the missing portion of the pattern and thereby ward off such IC failures.